OPTIONS

-h

Print an options summary page

-V

Print the rzip version number

-0..9

Set the compression level from 0 to 9. The default is
to use level 6, which is a reasonable compromise between speed and
compression. The compression level is also strongly related to how much
memory rzip uses, so if you are running rzip on a machine with limited
amounts of memory then you will probably want to choose a smaller level.

-d

Decompress. If this option is not used then rzip looks at
the name used to launch the program. If it contains the string
'runzip' then the -d option is automatically set.

-o

Set the output file name. If this option is not set then
the output file name is chosen based on the input name and the
suffix. The -o option cannot be used if more than one file name is
specified on the command line.

-S

Set the compression suffix. The default is '.rz'.

-f

If this option is not specified then rzip will not
overwrite any existing files. If you set this option then rzip will
silently overwrite any files as needed.

-k

If this option is not specified then rzip will delete the
source file after successful compression or decompression. When this
option is specified then the source files are not deleted.

-P

If this option is specified then rzip will show the
percentage progress while compressing.

INSTALLATION

Just install rzip in your search path.

COMPRESSION ALGORITHM

rzip operates in two stages. The first stage finds and encodes large
chunks of duplicated data over potentially very long distances (up to
nearly a gigabyte) in the input file. The second stage is to use a
standard compression algorithm (bzip2) to compress the output of the
first stage.

The key difference between rzip and other well known compression
algorithms is its ability to take advantage of very long distance
redundency. The well known deflate algorithm used in gzip uses a
maximum history buffer of 32k. The block sorting algorithm used in
bzip2 is limited to 900k of history. The history buffer in rzip can be
up to 900MB long, several orders of magnitude larger than gzip or
bzip2.

It is quite common these days to need to compress files that contain
long distance redundancies. For example, when compressing a set of
home directories several users might have copies of the same file, or
of quite similar files. It is also common to have a single file that
contains large duplicated chunks over long distances, such as pdf
files containing repeated copies of the same image. Most compression
programs won't be able to take advantage of this redundency, and thus
might achieve a much lower compression ratio than rzip can achieve.

HISTORY

The ideas behind rzip were first implemented in 1998 while I was
working on rsync. That version was too slow to be practical, and was
replaced by this version in 2003.

BUGS

Unlike most Unix compression programs, rzip cannot compress or
decompress to or from standard input or standard output. This is due
to the nature of the algorithm that rzip uses and cannot easily be
fixed.